Re: [PATCH] Unbuffer stdout and stderr on windows

[Christopher Faylor <cgf-use-the-mailinglist-please@sourceware.org>]

On Tue, Jul 23, 2013 at 08:51:53PM +0300, Eli Zaretskii wrote:
>> Date: Tue, 23 Jul 2013 14:34:32 +0800
>> From: Yao Qi <yao@codesourcery.com>
>> CC: <gdb-patches@sourceware.org>
>> 
>> On 07/22/2013 11:40 PM, Eli Zaretskii wrote:
>> > This is wrong, stdout should be line-buffered by default.
>> >
>> 
>> stdout is line-buffered if it can be detected to connect to an 
>> interactive device, otherwise it is fully buffered.  Cygwin emulates pty 
>> with pipes, and native win32 apps blindly assume all pipes are 
>> non-interactive.
>
>Sorry, I was unclear: I meant that stdout should be line-buffered, not
>unbuffered, when it is connected to a console (which is the default).
>I was under the impression that you were changing stdout to be
>unbuffered even in that default case, i.e. even when stdout is
>connected to a console.  If that's not so, i.e. if you were changing
>the buffering only when stdout is not connected to a console, I
>apologize for my misunderstanding.
>
>> > Also, this punishes batch mode with stdout redirected to a file: its
>> > stdout buffering (and perhaps also that of stderr, although that's
>> > less important) will now always be line-buffered, i.e. less efficient.
>> 
>> Yeah, this patch hurts the performance, but gets the outputs in the 
>> correct order, so that testsuite can be run to get a reasonable test result.
>
>I don't think it's right to penalize users for the benefit of the test
>suite.
>
>> > Is it possible to detect the "Cygwin ssh session", whatever that
>> > means, and only do this then?  I don't think it's right to change
>> 
>> Unfortunately, I am unable to find a heuristics to tell "GDB is in 
>> cygwin session".  There are some differences on env variables between 
>> cygwin and Windows cmd.exe console, but I am afraid that they are not 
>> reliable.
>
>Then how about introducing a special option which will cause the
>buffering to be what you want?  The test suite could use that option,
>and the other users will not suffer any penalty.
>
>> > behavior of a native w32 GDB just because it misbehaves when mixed
>> 
>> This patch is to change the buffered output to unbuffered, so the 
>> behaviour of GDB is not changed, IMO.
>
>Of course it's changed: buffering is user-visible behavior.
>
>> In the last resort, we may add an option "--cygwin-tty"
>
>I think this is the best alternative.
>
>> which I don't really like.
>
>Why not?

Note that this is only a problem for non-Cygwin versions of gdb.  It
sounds like someone is using mingw-built versions of gdb in a cygwin
pty session.  This obviously wouldn't be something that Cygwin itself
would need.

How about a "--buffer-output" option instead, which defaults to true?

cgf